Solid Superacid Of Tin In The Oxidation Reaction

Solid superacid SO₄^2-/SnO₂ (H₀ < -16) has been used in isomerization, alkylation, acylation, polymerization, oligomerization, esterification, oxidation, etc. It can be said that solid acids are the most important heterogeneous catalysts used today. The conventional catalysts are Lewis acid (AlCl₃, FeCl₃, TiCl₄, BF₃, etc) and proton acid (HF, H₂SO₄, HCl), but these catalysts have many disadvantages, such as bad selectivity, more side reaction, low yield, strong corrosion, difficulty in separation and recovery, serious environmental pollution etc. Solid acids are green industrial catalyst that is helpful to recycling and possesses wide prospect of application. Catalytic oxidations of hydrocarbons using oxygen or air as oxidants are significant and economical to the chemical industry.In this article, the basic knowledge of development and species of the solid superacid (especially SO₄^2-/SnO₂) and oxygenation of alkanes is introduced and reviewed. The content of this subject study is presented on the basis of studies on solid superacid and oxygenation of alkanes. The direct oxidation of n-heptane to ester using air as the oxidant under mild conditions assisted by solid superacid SO₄^2-/SnO₂ and metal-promoted sulfated tin oxide catalysts SO₄^2-/SnO₂-M_XO_Y (M= Ce, Co, V, Mo, Ti). The major aspects of the present study are as follows:(1) In the first part of this article, catalyst prepared by chemical co-precipitation method and characterized by means of SEM, XRD, BET, FT-IR and XPS techniques was studied.(2) Catalytic SO₄^2-/SnO₂ activity was tested for the directly oxidation of n-heptane. Products were analyzed with an on-line gas chromatograph-mass spectrometry. Under airtight conditions, main products are C-number of n-alkane from C₁₄ to C₂₂; under aeration conditions, oxygenate compounds presented. Some products such as: diisobutyl phthalate, cyclohexylmethyl tridecyl oxalate and 2-isopropylcyclohexanol that have not been reported in the directly oxidation of alkane by traditional method have been obtained, and all the products are used in fuel, leather, textiles, cosmetics and so on.(3) Metal-promoted superacids SO₄^2-/SnO₂-M_XO_Y (M= Ce, Co, V, Mo, Ti), which were highly active for this reactions, were investigated in order to improve its acid sites activity, selectivity and stability.(4) The introduction of Ti into SO_<sup>2-/SnO₂ can increase its surface area greatly. SO₄^2-/SnO₂-TiO₂ shows a certain photocatalytic activities in n-heptane oxidation using air as the oxidant in the presence of UV light. This new application of solid superacid also sets light on its special characteristics and its application field.(5) Finally, the article discussed the possible mechanism of these reactions.Compared with catalytic oxidations of hydrocarbons by traditional methods, simple work up procedure, milder reaction conditions, and shorter reaction times are the advantages associated with the SO₄^2-/SnO₂-M_XO_Y catalyzed processes. The present study revealed that SO₄^2-//SnO₂/M_XO_Y as a heterogeneous catalysis might hold great promise in the development of oxygenation of alkanes.